Design of a Wideband Tripolarized Antenna With High Isolation and Diverse Patterns

In this letter, a high-isolation wideband tripolarized antenna with broadside and monopole-like radiation patterns is proposed. It consists of a four-element circular loop array and two orthogonally-positioned dipoles. The crossed dipoles generate
$\pm \text{45}^{\circ }$
linearly polarized (LP) broadside radiations while the vertically LP omnidirectional patterns are produced by the loop array. To lower the operating frequencies and simultaneously expand the bandwidth, four groups of slots are first introduced in the
$\Gamma$
-shaped Balun design and second four narrow circular ring strips are added to arms of dipoles. For verification, a tripolarized antenna was fabricated and measured. Experimental results demonstrate that the proposed antenna obtains a wide overlapped band operating from 3.5 to 5.4 GHz with port-to-port isolation higher than 30 dB in most of the band. Directional and symmetrical patterns are attained for the dipoles and also the omnidirectional radiation patterns are maintained for the vertically polarized loop array across the entire band. Furthermore, the antenna yields measured peak gains of 8.8, 8.2, and 6.9 dBi in two broadside modes and monopole-like mode, respectively.